This application claims priority under 35 U.S.C. xc2xa7119 and/or 365 to 9801950-8 filed in Sweden on Jun. 2, 1998; the entire content of which is hereby incorporated by reference.
The invention relates generally to line interface boards and more specifically to minimizing the power consumption of line circuits on a line interface board.
In a subscriber line interface circuit driving a two-wire line, the line voltage as well as the line current is a function of the line load, i.e. the resistance of the telephone set and the line itself
When the line is open, the line is supplied with a maximum voltage at the same time as the current is zero. In order for the line circuit to operate, it must have access to a supply voltage which is somewhat higher than the required line voltage.
When the line is closed, i.e. when the line is loaded, the line voltage will decrease while the line current will increase depending on the sum of the line resistance and the load resistance.
The difference between the supply voltage and the line voltage will be applied across the line circuit through which the line current flows. This causes power consumption in the line circuit.
The power consumption in the line circuit will be highest for short lines, i.e. for a low total value of the resistances of the line and the load.
In many cases. the power consumption or power loss is accepted in the line circuit.
In some cases, a DC/DC converter can be used for each line to keep the maximum power consumption low. The output voltage from the respective converter is continuously controlled in order to be adapted to the instant line load. However, the use of such converters causes disturbing radiation and increased complexity of the circuits.
From WO 96/15617, it is known to use a number of analog series regulators corresponding to the number of driving voltages to minimize the power consumption by switching the supply voltage to the supply voltage having an absolute value which for the moment is the lowest adequate supply voltage.
When using line circuits with the above switching arrangement with e.g. two supply voltages, the voltage having the lower absolute value is set to a fixed predetermined value for which the least power consumption is expected. This predetermined value is usually set for all line interface boards. The voltage having the higher absolute value, is usually the battery voltage.
The object of the invention is to further minimize the power consumption of line circuits on line interface boards.
This is generally attained in accordance with the invention by adaptively adapting the supply voltage in response to the actual line voltages.
Hereby, it will be possible to further reduce the power consumption in line circuits on line interface boards.